Jet engine noise suppression system

ABSTRACT

A noise suppression system for testing jet engines includes both an intake silencer and an exhaust noise suppressor. The latter is designed to remove energy from the exhaust gases by cooling them quickly and to this end provides an acoustical tubular shell with a removable liner which provides a water-cooled coil for absorbing thermal energy from the gases. The coil is part of a water circulation system which includes a cooling tower or other means through which the water is circulated to cool it, thereby permitting operation of the system over an extended period of time. At the anterior end of the shell is a housing having a sonically sealable opening which receives the tail pipe of the jet engine. This housing provides also a tortuous intake passageway for secondary air, which is fed to a concentric augmenter tube extending into the anterior end of the shell.

United States Patent 1191 Smith et al.

1541 .IE'I ENGINE NOISE SUPPRESSION SYSTEM [751 Inventors: Cloyd I).Smith, Pacific Palisades; James H. Schmidt, Berkeley, both of Calif.

[73] Assignee: General Acoustics Corporation, Los

Angeles, Calif.

[22] Filed: Aug. 17, I970 [21] Appl. No.1 64,494

Related US. Application Data [63] Continuation-in-part of Ser. No.766,910, Oct. 11.

1968, Pat. N0.3,525,4l3.

[52] US. Cl. ..18I/33 I-IC, 181/33 HD, 181/52 [51] Int. Cl. ..B64d33/06, FOln 1/14, FOln 7//18 [58] Field of Search....l8l/33 HB, 33 HC,33 HD, 33

K, 181/43, 51, 52, 33 HE [56] References Cited UNITED STATES PATENTS2,685,936 8/1954 Brenneman et a1 ..181/-33 HC 2,798,743 7/1957 Olesten...l8l/33 HC 2,810,449 10/1957 Coleman..." ....181/33 HC 2.940.5376/1960 Smith ct a1. ....181/33 HC 3,174,581 3/1965 Duthion ct al.....l8l/33 HB 3,185,252 5/1965 Lemmerman...... ....18l/33 HC 3,187,8356/1965 Smith ....l8l/33 HC 3.208.552 9/1965 Scil'ert 181/33 H( m3,715,009. 1451 Feb. 6, 973

3.45:4,003 7/1969 Bcnharn ..181/33 HC FOREIGN PATENTS OR APPLICATIONS1,185,236 2/1959 France ..l81/33 HB 1,187.245 3/1959 France ..l 81/33 HC774,550 5/1957 Great Britain .....181/33 PIC 847,482 9/1960 GreatBritain 1 81/33 'HC 865.421 4/1961 Great Britain ..1 8 1/33 HC PrimaryExaminer-Robert S. Ward. Jr. Attorney-Forrest J. Lilly [57] ABSTRACT Anoise suppression system for testing jet engines i'ncludes both anintake silencer and an exhaust noise suppressor. The latter is designedto-remo'vej'energy from the exhaust gases by cooling them quickly and tothis end provides an acoustical tubular shell with a removable linerwhich provides a water-cooled coil for absorbing thermal energy from thegases. The coil is part of a water circulation system which includes acooling tower or other means through which the water is circulated tocool it; thereby permitting operation of the system over an extendedperiod of time. At the anterior end of the shell is a housing having asonically scalable opening which receives the tail pipe of the jetengine. This housing providesalso a tortuous" intake passageway forsecondary air, which is fed to a con-' centric augmenter tube extendinginto .the anterior end of the shell.

5 Claims 18 Drawing Figures l PAIENTEDFEB e um SHEET 10? 4 PATENTEDFEB 6I975 SHEET 2 OF 4 \SQQ Q PATENTEDFEB 61973 3.715.009

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. INVENTORS 61 0 v0 2 5144/ 7/4 d a /5 H 561 /44/07 .IET ENGINE NOISESUPPRESSION SYSTEM CROSS REFERENCE TO RELATED APPLICATION Thisapplication is a continuation-in-part of our parent application entitledNoise Suppression System," Ser. No. 766,910, filed Oct. 11, I968, andnow US. Pat. No. 3,525,4l 8, issued Aug. 25, 1970.

BACKGROUND OF THE INVENTION The present invention relates generally tomeans for absorbing quickly the sonic energy of a high velocity streamof gases to reduce the sound produced thereby, and is more particularlyconcerned with a structure designed to absorb and dissipate noisecreated during testing of jet engines in aircraft and the like.

The reactive propulsion engines, such as the gas turblue or the ram jet,produce a large amount of noise, both at intake and exhaust, as a resultof the high velocities at which air or exhaust gases are moving, Thefrequency range of the noises produced by operating engines of thisclass includes not only the entire audible range but frequencies whichare below and above the audible range. Because of the high intensity ofthe noise produced by these engines, these noises have definitelyinjurious physiological effects on nearby personnel; and this has led tothe problem of protecting personnel operating in the immediate vicinityof an engine. Running engines during ground testing and other groundoperations create serious occupational hazards for test personnel.

Reduction of the noise produced by an engine to a tolerable level can beaccomplished by absorbing the sonic energy. Speaking generally, this canbe accomplished by reducing as rapidly as possible the energy content ofthe exhaust stream and'then discharging the exhaust gases into theatmosphere at a greatly reduced velocity as compared with the velocityat which they issue from thejet engine exhaust.

accomplished by adding atmospheric air to the exhaust stream. Additionalcooling andenergy absorption has been accomplished in known types ofsound suppressing systems by spraying water directly into the stream ofexhaust gases after the initial cooling by the introduction of secondaryair. Maximum cooling is desired not only to extract sonic energy andthus reduce noise, but also to lengthen as much as possible the life ofthe acoustical shell. The use of water sprays is objectionable forvarious reasons mentioned in our above-identified parent application,which is directed to and claims a closed-water recirculation systemusing an internal cooling tower.

It is a general object of the present invention to devise novel andimproved means for: suppression of noise from the points of gas streamand secondary air intake into such a jet noise suppressor system. Thepresent purpose is not, however, restricted to systems utilizing water.cooling, through water cooling is preferred. The invention providesspring closure means, including sound sealing devices, at the head endof a jet engine noise suppressor for receiving and closely engaging thetail pipe of a jet engine, and for-accommodating to change of elevationof the latter with increased jet discharge, and provides also novelsecondary air entrance means acoustically contrived to suppress emissionof noise from the points of secondary air intake.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 4 is an enlarged verticalfragmentary section on line 44 of FIG. 3;

FIG. 5 is an enlarged detail in section of the area within the circle 5of FIG. 3;

FIG. 6 is an enlarged detail in section of the construction of themanifold within the circled area 6 of FIG. 9;

FIG. 7 is a combined end elevation and section of the water-cooled coiltaken on line 7-7 of FIG. 8;

FIG. 8 is a side elevation of the water cooling coil of the exhaustsuppressor;

FIG. 9 is a flow diagram of the coolingcoil of FIG. 8;

FIG. 10 is a section through the elbow illustrating a modified form ofturning vanes;

FIG. 11 is a section on line ll-llof FIG. 10;

FIG. 12 is a diagrammatic elevationas seen in the direction of thearrows l2--l2 in FIG. 3;

FIG. 13 shows a modified silencer somewhat similar to that of FIG. 3,the front end enclosure or housing being shown in vertical mediallongitudinal section, and a fragmentary portionof the tubular shellappearingin elevation;

FIG. 14 is a view taken in the direction of the arrows l4l4 of FIG. 15;

FIG. 15 is a view similar to FIG. 14, but enlarged, and with portions ofthe structure broken away to reveal underlying parts;

FIG. 16 is a view looking towards the left in FIG. 15, with certainparts broken away; I

FIG. 17 is a view taken as indicated by line 17-17; and- FIG. 18 isanenlarged sectional view within the area 18 of FIG. 13.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring now to the drawings, andmore particularly to FIG. 1, there is shown therein a jet aircraft Awhich has been brought into a position such that the noise suppressorsystem can be applied to it. Generally speaking, the system comprisestwo main units: an'inlet silencer indicated generally at l0 and theexhaust noise suppressor indicated generally at 12.

The inlet silencer consists of a pair of side shields 14 mounted upontracks 15 which enable the shields to be brought into contact with theaircraft at opposite sides thereof. The front andsidewalls of theshields are of acoustic construction and are designated to absorb thesound generated at the inlet end of the air ducts 16 leading to theengines of the aircraft. Any of various well-known wall constructionsmay be used for this purpose.

' Thecmain air inlet in the silencer for the engines is at the bottom ofthe two shields 14. As may be seen in FIG. 2, the rear end of eachshield is provided with a screened opening 17 designed to permit a largevolume of air to enter the space enclosed by shields 14 but to removeany harmful particles of foreign matter. The shields are also openunderneath the fuselage of the aircraft and screening at 18 is acrossthis air'inlet opening. A minor air inlet isalso preferably provided atthe forward end of the two shields, as may be seen in FIG. 1, by leavinga space 19 between the two shields underneath the nose of the aircraft.The sideand front walls of the shields 14 are of acoustic constructionso that the open ends of air ducts 16 are substantially enclosed, exceptas necessary to admit air for the engines.

The front walls 14a of the shields 14 are in effect targets againstwhich'sound generated at air intakes 16 impinges. By making these wallsof acoustic construction, much of the intake-generated sound, especiallyobjectionable highfrequencies, is absorbed. When one engine is running,the opposite intake unit acts as an additional acoustical absorptivechamber.

The exhaust noise suppressor indicated generally at 12 receives the highvelocity stream of exhaust gases from the jet engine or engines in thetail of the aircraft. The tailpipe or exhaust duct of the aircraft isindicated at 20 in FIG. 3 which shows the exhaust noise suppressor indetail.

The stream of hot exhaust gases leaving tailpipe 20 enters augmentertube 21 which is axially aligned with tailpipe 20. The tailpipe issmaller in diameter and may be spaced slightly from the entrance to tube21 so that surrounding secondary air is drawn into the inlet end of tube21 by injector action from the exhaust stream.

It is preferable to add to tube 21 a-second augmenter tube 22 of largerdiameter than tube 21 that provides a second inlet for surrounding air,also by injector action. Thus, there is a mixture of the exhaust gasesand secondary air passing through the augmenter assembly comprisingtubes 21 and 22. The secondary air cools the high temperature exhaustgases and the mixture is discharged from the end of tube 22 into tubularshell 24 which is a means for obtaining further cooling of the gasstream.

The inlet end of the augmenter assembly is located within enclosure 25which traps and absorbs sound 7 energy of the exhaust stream whichescapes at the inlet of the augmenter assembly. Enclosure 25 has anupwardly facing air inlet 26 for secondary air, the air passing downaround an internal baffle 27 which traps sound in this region byproviding tortuous paths for the incoming air downwardly within theenclosure 25 to the inlet ends of the two tubes 21 and 22. The augmentertubes 21 and 22 have bell mouths and a partition 23 may be used todivide the secondary air flow into a portion entering augmenter 21 andanother portion entering augmenter 22. Optimum cooling can be obtainedby longitudinally adjusting the augmenter tube 21 to control theproportion of air entering the two tubes. The augmenter tube 21 can forthis purpose be placed on a mounting structure 21a having roller means21b movable along a track 21c. In such case, of

course, the partition 23 must be arranged to accommodate such movement;it can, however, and generally is, simply omitted, as in FIG. 13.Alternatively, the augmenter tube 21 can be adjusted longitudinally onits rollers, and a partition such as 23 installed afterwards.

The escape of sound at the point of entry of tailpipe pipe duringvarious power settings. A simple diagram- 1 matic showing of such springloading appears in FIG. 12, where springs s on brackets b engage theupper and lower halves of the seal, and can yield and elongate,respectively, as the case may be, as the tailpipe tends to rise or fall.A more detailed disclosure, together with preferred means for moving thehalves of the seal toward and from one another, and the addition of asound trap, are shown in the modification of FIGS. 13 18. The structuresof these FIGS. may of course be incorporated in the silencers of FIGS. 1and 3.

From augmenter tube 22, the exhaust gases, now partially cooled, enterthe cooling chamber within shell 24. Shell 24 is preferably circular incross section and has an annular wall of acoustical material whichprovides a high degree of energy and noise absorption. While the wallmay have any desired construction and thickness, the preferredconstruction is illustrated in FIGS. 4 and 5. In these figures, it willbe seen that the innermost element of the wall is a perforated sheet 30.Outwardly of this sheet is a corrugated sheet 31 which is alsoperforated metal. Outwardly of corrugated sheet 31 is a zone 32 which isfilled with fibrous high temperature sound absorbent material, such asglass fibers, or rock wool. The zone 32 is preferably composed of aplurality of layers of fibrous material of outwardly increasing densityin order to render the wall most effective over a wide range of soundfrequencies. On the outside, the wall is covered with a solid metalplate 34. All of the materials for the wall of shell 24 are selected towithstand the elevated temperatures encountered.

Inside shell 24 is a gas cooling coil, indicated generally at 35, whichserves as a liner for shell 24 and defines the main passage for exhaustgases through the cooling chamber within the coil. The cooling coil isshown in detail in FIGS. 7 and 8, while water circulation and theconnections between the various elements of the coil are showndiagrammatically in FIG. 9.

The gas cooling means, identified generally at 35, and referred toherein as the cooling coil, comprises a longitudinally extendingfoundation means which, for reasons that will become apparent, isdesigned to operate in the manner of a skid, and upon which a pluralityof individual annual pipes or turns of the cooling coil are supported.Actually, it is preferred to take advantage of the presence of thestructural members at the bottom of the cooling coil forming the baseelements to utilize these members as manifold means to distribute thecooling water to the several individual coils. These considerations leadto the preferred design, although it will be understood that theinvention is not necessarily limited to all of the details of thispreferred embodiment of the coil.

As shown in FIGS. 7 and 8, at the bottom of the cooling coil 35, thereis a pair of longitudinally extending pipes 37 and 38. Although thesepipes are in effect segmented in order to function as manifold means aswill be described, the successive segments in each pipe are axiallyaligned and connected together to form a structurally unitary member inorder that the two pipes 37 and 38 provide the foundation or base onwhich the coil as a whole is supported. Connected to the two pipes 37and 38 are a plurality of small annular tubes or hoop-like pipes 40, thediameter of these turns being such that coil assembly 35 is receivedwithin shell 4 with some clearance between the pipes 40 of coil 35 andinner wall 30 of the shell, except at the bottom of the shell wherelongitudinal members 37 and 38 contact the shell.

The individual pipes 40 or turns of the cooling coil are preferablyspaced from each other and also from the. inside surface of the wall ofshell 24, as shown in FIG. 5. This permits more complete exposure of theexterior surface of tubes 40 to the heated. gases passing through thecooling chamber, thereby increasing the rate of heat exchange betweenthe gases and the pipes 40. Also, the spacing of the pipes from theshell walls cools the gases that reach the shell wall and thus reducesthe maximum gas temperatures to which the shell is exposed. Thistemperature reduction, as compared to a shell with water sprays and nocoil 35, results in a greatly extended life of the equipment. Based onobservations to date, it appears that the useful life of a suppressorshell may be increased by a factor of as I much as five. It has alsobeen found that the spacing of the cooling tubes, in combination withthe absorptive liner, results in a modified resonating chamber resultingin an increase in low frequency attenuation.

Incorporated in the wall of shell 24 are a plurality of support pads 42,as shown in FIG. 4. These are located at the bottom of the shell and arespaced at suitable intervals longitudinally ofthe shell to support coil35 with the two pipes 37 and 38 resting upon pads 42. In posi tionwithin this shell, the coil assembly is held in place by clamps 43 whichcan be tightened down against pipes 37 and 38. 7

However, when clamps 43 are loosened and the. inlet and outlet waterconnections to the coil are disconnected, coil 35 as a whole can slideinto and out of shell 24; and it is to facilitate this movement of thecoil as a whole that the two'pipes 37 and 38 are made of structurallycontinuous members. Alternatively, pads 42 can be replaced by a singlecontinuous support extending lengthwise ofthe shell. I

In order to obtain manufacturing economies of production. and forobvious engineering reasons, cooling coil 35 is made of the samediameter throughout its length, as is also tubular shell 24. However, itwill be understood that the invention is not necessarily limited tothisdesign.

Water flow within coil 35 isshown schematically in FIG. 9. Supply line45 is connected to one end of pipe 37 while outlet 46 is atthe oppositeend of the same manifold pipe. Rapid contours transfer from the gases tothe water within the tubes 40 requires a large surface area in contactwith the gases. This can be obtained by a large number of tubes 40 ofrelatively small diameter, as opposed to smaller number of tubes oflarger diameter. At the same time, reduction in the diameter of thetubes increases the resistance to water flow and reduces the quantity ofwater flowing through a tube past a given point per unit time. For thisreason, the coil is not made up of a single length of tubing arrangedhelically but instead the individual pipes 40 each extend for a singleturn and extend between one manifold section in pipe 37 and anothermanifold section in pipe 38; and the individual pipes 40 are arranged ina number of groups in parallel with water flow in one direction withineach group.

Assuming for purposes of illustration that there are four groups ofpipes 40, each occupying approximately one fourth of the length of coil35, water enters pipe 37, through supply line 45. At approximately thequarter point of the coil, barrier 47'closes manifold pipe 37 so thatflow from right to left in pipe 37 is limited to initial manifoldsection 370. All of the annular pipes 40 are connected to manifold 37aare thus supplied water which flowsthrough'them to the initial manifoldsection 38a of the opposite manifold pipe 38. Water then flows to theleft within manifold section 38a to the second group of pipes 40, flowbeing limited in pipe 38 by barrier 48. As a result, in the second groupof pipes 40, flow is from manifold 38 back to manifold 37. Flow enteringthe second manifold segment 37b now flows within that segment to a pointwhere flow is limited by a further barrier 49 and water flows throughthe third group of pipes 40 from manifold 37 back to the second segment38b of manifold 38. Continuing this zig-zag pattern of flow betweenmanifolds, water leaves the second manifold section 38b to return to thefinal segment 370 of manifold 37 and then out of the coil at outlet 46.

When pipes 40 are divided into aneven number of groups, here there arefour, the water outlet line will be connected to the same manifold asthe supply. Were the pipes 40 arranged in three groups, then waterdischarge line 46 would be connected to the end of manifold segment 38b.From inspection, of FIG. 9, it will be seen that some of the pipesegmentsare longer than others, and each segment may be regarded byitself as a manifold'. The first and last segments through which thewater flows are connected to only one group of pipes 40 and areconsequently shorter than the intervening segments of the manifoldwhichare each connected to two groups of pipes 40. l

From the standpoint of water flow and distribution, each of the segmentsof the individual manifolds 37 and 38 is a separate manifold as far asthe flow pattern is concerned, distributing water to and/or receivingwater from a group of pipes, there being preferably an equal number ofpipes 40 in' each group. However, pipes 37 and 38 are each referred toas a manifold since they have structural integrity which permits them tooperate as support members for the coil as a whole, as

described above.

Thus, it will be seen that viewed from one standpoint each of manifolds37 and 39 may be regarded as a continuous pipe with plugs at intervalsto localize water flow within the pipes. From another viewpoint, eachsegment of these two members may be viewed as a complete manifold unitadjacent another similar unit. This arises from the dual functions ofthe pipes 37 and 38, as explained.

At the end of shell 24 opposite augmenter tubes 21 and 22, the nowconsiderably cooled gases are discharged. The gases are still hot enoughthat discharge in a horizontal direction is undesirable; and,consequently, it is preferred to connect the end of the shell to anelbow structure illustrated in FIG. 3 as comprising three principlesections. The elbow includes two sections 51 and 52, each of which hasan end face. with a connecting flange lying in a radial plane normal tothe section axis and at the opposite end a face lying in a plane at 45to the section axis. These latter two faces are each connected tointermediate section'53 which is elliptical in outline and which carriesinternally a plurality of gas turning vanes 55. The three sections ofthe elbow are conveniently welded together to form a unitary structure,and the elbow is connected to shell 24 in such a position that gasesdischarged are directed upwardly into the atmosphere.

If desired, the gas discharge from elbow section 52 can be carriedfurther upwardly into the air by a stack 55 on thedischarge end of theelbow.

Additional cooling of the gas can be effected and the walls of the elbowcan be protected against excessive heat by providing cooling in the formof a water jacket for'each of sections 51, 52, and 53 of the elbow, asshown particularly in FIG. 3. In each section, the jacket is formed byproviding a double wall for the elbow with space between the two wallsto receive water which circulates within the space.

To permit operation of the exhaust noise suppressor over an extendedperiod of time, means are provided for cooling and circulating waterthrough coil 35 and the elbow sections. The circulation system isillustrated diagrammatically in FIG. 3. This circulation system consistsof a reservoir or surge tank from which water may be taken through lines61 and pumped through coil 35 and the jacket on the elbow structure bymain circulation pump 62. The discharge side of pump 62 is connected byline 63 directly to supply line 45 to cooling coil 35. Branch lines 64and 65 each supply water to one of the water jackets of elbow sections51 and 52, respectively, the connections to the water jackets being at alow point on the jackets and remote from the outlet, to be mentioned.Another branch supply line 66 supplies water to the jacket ofintermediate elbow section 53.

The three separate water jackets on the three elbow sections 51, 52, and53 are placed in communication with each other near outlet by a pair ofopenings 68 in the interconnecting flanges. As a consequence, the singledischarge line 71 connected to outlet 70 receives heated water from allthree jacket sections-Line 71 is connected at 72 to discharge line 73which is connected to outlet 46 from coil 35. Line 73 returns the heatedwater from the noise suppressor to reservoir 60.

In order to cool the water after return to tank 60, it is withdrawn formthe tank by pump 75 through line 77 which delivers the discharge frompump 75 to cooling tower 78. From the sump at the bottom of the coolingtower, cooled water is withdrawn through line 80 by pump 81; and thedischarge side of pump 81 is connected to line 61 so that the watercooled in the tower can flow directly to the intake side of maincirculating pump 62 without necessarily returning to the storage tank,although the storage tank is, in effect, continuously connected to thecirculating pump in order that there is always an adequate supply ofwater available to pump 62. A valved by-pass line 82 may be used toreturn cooled water to tank 60 if circulation through the suppressor isnot needed.

FIGS. 10 and 11 illustrate a variational embodiment of the invention inwhich additional cooling of the exhaust gas stream is achieved by watercooling of the turning vanes in the elbow. The outer wall of elbowsection 53 is water-jacketed as described. Turning vanes 85 are hollowto permit cooling water to pass through them. The vanes extend outwardlythrough the waterjacketed wall to connect to an inlet manifold 86 and anoutlet manifold 87. In turn, these two manifolds are connected to theclosed circuit for circulation of cooling water.

FIGS. 13 18 show a jet engine sound suppressor of the type of theembodiment described above, showing much of the structure of the earlierembodiment, together with certain improvements. Corresponding parts ofthe two embodiments will be designated by the same reference numerals,but with primes added in the case ofFIGS. 13 18.

The housing 25' of the embodiment of FIGS. 13 18 is of somewhatincreased height. It has an air inlet 26' at the top, located over thefront portion of the housing, and extending from the front edge of thehousing for somewhat less than half the distance from its front to itsrear edge. Below opening 26', the housing contains acoustic air baffles100, projecting alternately from the front and rearward housing walls.The projecting end portions of the baffles overlap one another, asshown, providing a tortuous path for the incoming airstream 101, andthus affording a sound trap against emission of noise. The walls ofhousing 25', including the baffles 100, are of acoustic construction,and thus tend to absorb rather than reflect sound impinging thereon. Atypical construction is shown in the crosssection of FIG. 18. An outsidesheet of sheet steel, say 11 gauge is bonded to a sheet 111 of hardboard, such as one inch thick gypsum board. Next to sheet 111 is a layer112 of mineral wool, against which is a flexible sheet 113 of glassfiber. Adjacent the later is a perforated sheet 114 of 11 gauge sheetsteel. Such an acoustic board has very high sound absorptioncharacteristics.

Augmenter tubes 21 and 22 are provided, in general as in FIG. 3. Theaugmenter tube 21' is on a support 21b having roller means 210 movablelongitudinally of the tube on a platform 21d. Thus, movement of the tube21' adjusts the proportion of secondary air into the two augmentertubes, an enables the optimum position to be found, at which cooling andnoise reduction are at a maximum.

In the front wall of air inlet housing or conduit 25' is a window 121,over and in front of which is mounted a rectangular frame 122. Thisframe is vertically slidable on stationary vertical rods 124 passingthrough its opposite vertical edge portions and secured to front housingwall 120 by brackets such as 125. An upper spring 126 encircles theupper horizontal frame member 127 on the underside, and engaging acollar 128 on the rod 124 at its lower end. Thus, the spring yieldinglysupports the frame 122 by engaging under the frame member 127. A lowerspring 128 encircles the rods 124 below the frame 122, and engages thelower brackets 125 at the lower ends of the springs. These spring thusalso yieldingly support the frame 122. The frame 122 floats on thesprings 126 and 128.

A pair of upper and lower seals or seal boards 130 and 131 are mountedfor vertical movement toward and from one another on the rectangularframe 127 and are formed on their contiguous edges with then 130a and131a, preferably added, to conform to close on the effect a seal to thetail pipe or pipes 133. These seals are mounted for movement toward andfrom one another to close, or separate from, the tail pipe or pipes 133.In the present preferred arrangement, the frame 122 is spring-supported,and' the seals are movable on the frame 122 to close snugly on the tailpipe. Thus, as the tail pipe tends to rise, the seal boards willelevate, taking some of the loading off the springs. If the tail pipethen tends to lower, under decreased power, more of its weight isreimposed on the frame 122, through the seals 130 and 131, and the frame122 lowers accordingly.

The presently illustrated means for moving the seals 130 and 131relatively to the frame 127 embodies threaded vertically aligned nuts orlugs 140 on the seals, in which are received oppositely pitched halvesof lead screws 142. The latter may be rotated simultaneously, in thesame direction, by any suitable means, e.g., a hand wheel 160 operatingthrough an angle gear drive 1 61 mounted on the frame 122 and driving ajack shaft 164 driving the two lead screws through angle drives 166. v

Thus the two seals may be closed on the tail pipe or pipes by operationof the hand wheel 160; and it will be seen that the springs 126 and 128spring-load the seals to move vertically to accommodate verticalmovement of the tail pipe or pipes at various power settings of the jetengines exhausting through the tail pipes.

Unique noise shields are also preferably provided to seal against escapeof noise about the seals 130 and 131 and the supporting structuretherefor. These are shown in FIGS. 14, 15, 16, and 17 but omitted forclarity in FIG. 13. Two vertical sheet steel members 180 ofsubstantially Z shaped cross section are mounted on the front wall 120of housing 25', and have flanges 181 overhanging vertical edge portionsof frame 122 (FIG. 17). These members arelined with sound absorbingmaterial 183. Inside and interengaging with, as well as slidable along,the flanges 182, are the flanges 184 of substantially Z-shaped members185, also acoustically treated with sound absorbent material in areasexposed to jet noise. The flanges 184 of these members 185 engage andare secured to the sides of the frame 122, and

the members 185 stand outwardly therefrom and, with relatively closelyreceive the shield flanges 187. Between the flanges 187, the insidesurfaces of portions 192 are treated with acoustic absorbent material asat 194. These provisions are effective in reducing noise otherwiseemanating from the structure which surrounds and closes on the tailpipes.

From the foregoing description, it will be realized that various changesin the detailed construction and arrangement of the noise suppressorsystem may occur to persons skilled in the art without departing fromthe spirit and scope of the present invention. Accordingly, theforegoing description is considered as being illustrative of, ratherthan limitative upon, the invention disclosed herein.

We claim:

1. In a-jet engine noise suppressor for receiving and reducing the noiseof exhaust gases discharged from the tail pipe of the engine,

a tubular noise suppressor shell for conducting the exhaust gasesdischarged from said tail pipe,

a housing structure at the anterior end of said shell including anapertured front wall and seal means movable thereon and supportedtherefrom for receiving and closing about said tail pipe and forming aseal with said tail pipe, said housing structure confining the exhaustgases on their way from said tail pipe to said anterior end of saidshell,

said seal means comprising a pair of seal members arranged to moverelative to said front wall and to close on said tail pipe by relativemovement.

toward one another, and spring loading means for yieldingly supportingsaid seal members with accommodation for vertical movement of the tailpipe at different power tail pipe of the engine,

a tubular noise suppressor shell for conducting the exhaust gasesdischargedfrom said tail pipe,

a housing structure at the anterior end of said shell including anapertured front wall and movable seal means thereon and supportedtherefrom for receiving and closing about said tail pipe and forming aseal with said tail pipe, said housing structure confining the exhaustgases on their way from said tail pipe to said anterior end of saidshell,

means forming a secondary air entrance passage open at one end to theatmosphere and discharging at the other in a region to become added tothe hot exhaust gases passing from said tail pipe to said anterior endof said shell, and

concentric annularly spaced augmenter tubes located in the anterior endof said shell for receiving and passing the hot exhaust gases from saidtail pipe into said anterior end of said shell in two divided columnsand for receiving said secondary air from said passage to mix with thetwo columns of said gas, one of said augmenter tubes being adjustablelongitudinally relative to the other.

4. In a jet engine noise suppressor for receiving and reducing the noseof exhaust gases discharged from the tail pipe of the engine,

means supporting said augmenter tube for axialmovement longitudinally ofsaid shell.

5. The subject mater of claim 2, including also:

a vertically movable frame supported on said front wall or verticalmovement relative thereto, said frame having vertical edge portions,

said spring loading means reacting from said front' wall to yieldinglysupport said frame,

said pair of seal members being supported from said vertically movableframe and being movable toward and form one another relative to saidframe to close on said tail pipe,

a pair of vertical sound shield strips mounted on said front'wallalongside said vertical edge portions of said movable frame, said stripshaving vertical flanges turned toward one another,

a pair of vertical sound seal strips mounted on said vertically movableframe, adjacent to said vertical edge portions thereof, said lastmentioned strips having portions vertically slidingly engaging andacoustically sealed to said first mentioned strips, and having flangeportions forming edge channels slidably receiving vertical edge portionsof said seal members and being acoustically sealed thereto, and

a pair of horizontal sound shield strips mounted on said front wall,above and below said vertically movable frame, including web and flangeformation extending over and downwardly, and over and upwardly,respectively, relative to the respective upper and lower portions ofsaid movable frame and of said seal members.

1. In a jet engine noise suppressor for receiving and reducing the noiseof exhaust gases discharged from the tail pipe of the engine, a tubularnoise suppressor shell for conducting the exhaust gases discharged fromsaid tail pipe, a housing structure at the anterior end of said shellincluding an apertured front wall and seal means movable thereon andsupported therefrom for receiving and closing about said tail pipe andforming a seal with said tail pipe, said housing structure confining theexhaust gases on their way from said tail pipe to said anterior end ofsaid shell, said seal means comprising a pair of seal members arrangedto move relative to said front wall and to close on said tail pipe byrelative movement toward one another, and spring loading means foryieldingly supporting said seal members with accommodation for verticalmovement of the tail pipe at different power settings of the jetengine.
 1. In a jet engine noise suppressor for receiving and reducingthe noise of exhaust gases discharged from the tail pipe of the engine,a tubular noise suppressor shell for conducting the exhaust gasesdischarged from said tail pipe, a housing structure at the anterior endof said shell including an apertured front wall and seal means movablethereon and supported therefrom for receiving and closing about saidtail pipe and forming a seal with said tail pipe, said housing structureconfining the exhaust gases on their way from said tail pipe to saidanterior end of said shell, said seal means comprising a pair of sealmembers arranged to move relative to said front wall and to close onsaid tail pipe by relative movement toward one another, and springloading means for yieldingly supporting said seal members withaccommodation for vertical movement of the tail pipe at different powersettings of the jet engine.
 2. The subject matter of claim 1, whereinsaid seal members are movable vertically to close on the tail pipe, andsaid spring loading means act vertically on said seal members.
 3. In ajet engine noise suppressor for receiving and reducing the noise ofexhaust gases discharged from the tail pipe of the engine, a tubularnoise suppressor shell for conducting the exhaust gases discharged fromsaid tail pipe, a housing structure at the anterior end of said shellincluding an apertured front wall and movable seal means thereon andsupported therefrom for receiving and closing about said tail pipe andforming a seal with said tail pipe, said housing structure confining theexhaust gases on their way from said tail pipe to said anterior end ofsaid shell, means forming a secondary air entrance passage open at oneend to the atmosphere and discharging at the other in a region to becomeadded to the hot exhaust gases passing from said tail pipe to saidanterior end of said shell, and concentric annularly spaced augmentertubes located in the anterior end of said shell for receiving andpassing the hot exhaust gases from said tail pipe into said anterior endof said shell in two divided columns and for receiving said secondaryair from said passage to mix with the two columns of said gas, one ofsaid augmenter tubes being adjustable longitudinally relative to theother.
 4. In a jet engine noise suppressor for receiving and reducingthe nose of exhaust gases discharged from the tail pipe of the engine, atubular noise suppressor shell for conducting exhaust gases dischargedfrom said tail pipe, an augmenter tube extending axially into theanterior end portion of said shell for receiving and passing hot exhaustgases from said tail pipe inside thereof, the anterior end portion ofsaid tube and shell being annularly spaced from one another to form anannular secondary air intake port which opens into said gas passageway,and means supporting said augmenter tube for axial movementlongitudinally of said shell.